Relay system



Sept. 8, 1931. F. B. vFALKNOF: ET Al. '1,822,086

` RELAY SYSTEM Filed Sept. 13I 192e lo OIII lo NU l 9s MN m N lo o|| ,a Q WJ U H 5 m if W T a m; fw N 1MM /M w S m e P a M D@ v l gm m Wmfvnmm, EN ww n MQ XkMW Patented Sept. 8, 1931 FRANK-B. FALKNOR AND THADDEUS R.

GOLDSBOROUGH, OF WILKINSBURG, PENNSYL- VANIA, ASSIGNORS TO WESTINGI-IOUSE ELECTRIC AND MANUFACTURING COMPANY,

A CORPORATION 0F PENNSYLVANIA RELAY SYSTEM Application. filed September 13, 19%,6.A Serial No. 135,020.

Our invention relates to the art of radio transmission and reception, and it has particular reference to what are now known as relay systems, in which the signals received from distant points are used to control the operation of a local transmitting station.y

Many systems of this general type have been proposed in the past, the majority of which, insofar as We are aware, have re- "`quired the reduction of the incoming signal to an audio frequency, which frequency, after amplification, is employed to modulate the output of an` oscillation generator Y coupled to the.V radiation system. 15 l Relay systems which of necessity employ a plurality of stages of audio frequency amplification give an output in which the signal is to a great extent marred by a background of extraneous sounds, due to static, etc. Microphonic noises arising in the various tubes, batteries and other parts of the circuit are ampliiied by the audio frequency amplifiers and as a result, the quality of the re-radiated signals is poor.

Y t is accordingly an object of our invention to provide a relay system which will pass the signal on to the local radiation system `without the additional thereto of noises arising in the relay station circuits per se.

Another object is to provide a relay system which will be only slightly influenced by static disturbances.

Another object is to provide a relay systeni which will be substantially automatic in operation and which will re-radiate a wave of constant frequency.

Still another object is to provide a relay system which will re-radiate signals at the same frequency at which they are received, or at a frequency bearing an harmonic relation to the reception frequency.

A further object of our invention is to provide a relay system which may make use of piezo-electric means to control the frequency of the re-radiated signal.

These objects, and others which will be more fully explained later, we accomplish by changing the frequency of the incoming `signal to a definite lower frequency, which is preferably a sub-harmonic of the incoming carrier wave. Vve employ the term subharmonic to indicate that the new frequency bears a definite ratio to the old, regardless of which is the higher, and regardless of whether the ratio is expressible as an integer. The sub-harmonic frequency is amplified sufficiently to be transmitted from the local receiving station over land lines tol lthe local transmitting station,

where, after still further amplification, it is raised to correspond to the frequency of the incoming wave. The signal is again amplified at the high frequency and re-radiated from the local transmitting antenna.

Referring now to the drawings, from which, together with the following descrip-` tion, a more complete understanding of invention may be had:

Fig. 1 is a diagrammatic view of a preferred-form of our invention illustrating a complete receiving and re-transmitting station.

Fig. 2 is a diagrammatic view of a preferred form of frequency changer.

Fig. 3 is a diagrammatic view of a crystal` controlled harmonic generator.

Referring specifically to Fig. 1, a source 1 of incoming signals is coupled to an inductor 2, shunted by a condenser 3 which forms the input circuit of a vacuum-tube detector device 4. The device 4: is provided with a grid 5, a filament 6 and an anode 7 and has connected to the filament a heating battery 8.

An oscillation generator 9 has an output coil 11 which is coupled to the inductor 2. Between theanode 7 and the filament 6 are connected serially an inductor 12 and an anode battery 13, the latter being shunted by a by-pass condenser k141. Serially incof another beat-frequency amplifier 23, which has an output inductor 24.

An inductor 25 is variably` coupled to the inductor 24 and forms the input of a frequency changer 26. The output from this frequency changer 26 is led into a high-frequency amplifier 27 which has in its output an inductor 28, shuntcd by a variable condenser' 29. Conductively connected to the output circuit 28-29 is a choke 31 from which a conductor extends to the transmitting antenna 32.

Fig. 2 shows diagrammatically the circuits and apparatus which may be employed in connection with the frequency changer 26 of Fig. 1. The output inductor 24 is coupled to an inductor 25, shuntcd by a variable condenser 33. The circuit 25 33 is connected between the grid 34 and the filament 35 of a thermionic device 36. The device 36 is provided with an anode 37, and an inductor 38 and a high-potential battery 39 are connected between the anode and the filament 35. The thermionic device 36 is further provided with a grid-biasing battery 41. A piezo-electric crystal 42 is electrostatically associated with the output inductor 38.

A second thermionic device 43 is provided with a grid 44, a fiiament 45 and an anode 46. Connected between the grid 44 and the filament 45 is a choke 47. The input circuit of the device 43 is also electro-statically associated. with the crystal 42. Connected between the anode 46 and the filament 45 are an inductor 48 shunted by a condenser 49, and an anodebattery 51. The filament of the thermionic device 43 is heated by means of filament heating battery 52.

Fig. 3 is a diagrammatic view of a preferred form of the oscillation generator indicated by rectangle 9 in Fig. 1. Such an oscillation generator is fully disclosed and claimed in a copending application, Serial No. 78,115, in the name of Donald G. Little, filed December 29, 1925, and assigned to the Westinghouse Electric & Manufacturing Company. The oscillation generator comprises a plurality of thermionic devices 60, 61 and 62. The input circuit of the first device comprises a piezo-electric crystal 63, a choke 64 and a biasing battery 65. The output circuit of the device comprises an inductor 66 and a variable condenser 67.

Coupled to the output inductor 66 is the input circuit of the second thermionic device 61, which input circuit comprises a choke 68 andl abiasing battery 69. The device 61 is provided with an output circuit comprising an inductor k70 and a variable condenser 71, and this output circuit is, in turn, coupled to the input circuit of the device 62, which comprises a choke 72 and a grid biasing` battery 73. The output circuit of the device 62 is coupled to an oscillating circuit comprising inductor 74 and condenser 75.

In the operation of the harmonic generator shown in Fig. 3, each successive output circuit is tuned to a higher harmonic than the output circuit of the tube preceding it. For example, the first thermionic device 6() may have shunted across its input a crystal which is naturally resonant at 1,000 kilocycles and in that case the output circuit 66-67 would be tuned to 1,000 kilocycles, but, due to the inherent characteristics of the oscillating crystal circuit, many of the higher harmonics would also be present. If, in such event, the output circuit 70-71 of the next thermionic device 61 is tuned to 2,000 kilocycles, that frequency will be very markedly present therein. In the same manner, the output circuit 74--7 5 of the thermionic device 62 may be tuned to 4,000 kilocycles and this latter frequency may be used as a source for heterodyning. The operation and means involved in this type of crystal-controlled harmonic generator are very fully described in the copending application referred to and need not be more specifically described at this point.

In the operation of our rela)T system, the incoming signal is first heterodyned by the local oscillation generator to a definite lower frequency. Preferably, this lower frequency is a sub-harmonic of the incoming signal. To do this, use is made of the super-heterodyne principle disclosed in the patent to Armstrong No. 1,342,885. As is well known in the art, the beat frequency produced by the first detector will carry the signal-frequency modulations. In the usual form of super-heterodyne this beat frequency is passed through a plurality of tuned transformer stages and is then demodulated in a second detector device.

In the operation of our relay system, we pass this beat frequency through the usual beat-frequency amplifiers and then impress it upon the lines connecting the local receiving station to the local transmitting system.

At the local transmitting station, it is necessary to re-amplify the beat frequency and this is accordingly done in a series of stages indicated by the rectangle 23 in Fig. 1. The amplied beat frequency is then impressed upon the input circuit of a frequency changer which is so arranged that its output frequency will be a definite harmonic of the beat frequency and will preferably be the frequency at which the signals were first received.

The frequency changer may take the form shown in patent to Alexanderson 1,174,793, or may be constructed in a manner analogous to the disclosure of Kendall in patent No. 1,446,752.

We may also employ as a frequency suming that the incoming signal has a frequency of 3,000,000 cycles per second, the piezo-crystal will be so chosen as te have a frequency of 30,300 cycles per second, Which frequency is multiplied by the harmonic generator to a frequency of 3,030,000 cycles per second. This frequency of 3,030,- 000, reacting With the incoming signal of 3,000,000 cycles Willgive a beat frequency of 30,000 cycles, which isrectified by the first detector and passed into the beat frequency amplifier. The frequency changer kshown as rectangle 26 in Fig. l, is so adjusted that its final output Will be a harmonic at 3,000,000 cycles per second. It is thus seen that the incoming signal is first stepped down to a definite harmonic lower frequency Which maybe efficiently transmitted over land lines and. is then changed back to the original frequency for re-transmission by making use of harmonics.

The form of frequency changer shovvn in Fig. 2 Will be new described. The intermediate frequency is applied to the input circuit of a thermionic device which is tuned to that frequency. In the output circuit of this thermionic device is located an induetor shunted by a condenser,ithe dielectric of which is a piezo-electric crystal.

Vhen voltages at the fundamental frel quency of the crystal are set up across the crystal by reason of its connection in the output circuit of the first thermionic device, it will vibrate physically at a variety of harmonic frequencies as Well as at the fundamental frequency, its physical vibrations being accompanied by electric potentiall changes.

The desired harmonie is impressed on the Vinput circuit of another thermionic device through a second condenser, the dielectric of which is formed by a portion of the same piezo-electric crystal. The output circuit of the second thermionic device is tuned to the desired harmonic and may be coupled directly to the input circuit of a high frequency amplifier, or may be passed through a plurality of stages until any desired harmonic is obtained.

The crystal may be so cut and arranged that one portion thereof may be quite thick While another portion may have much smaller dimensions enabling it to vibrate at a much higher frequency than the thicker portion. We may also use a second and smaller crystal physically distinct from the main crystal but mechanically coupled thereto by Y an imbedded rod or other means.

It is apparent that VWhen the incoming frequency is not constant, the beat produced by the interaction of the output of the piezo-crystal controlled oscillation generator and the incoming frequency will not have a fixed relationship to the latter frequency. In that event, We may employ as an oscillation generator a device, the frequency of Which is determined by the incoming signal, and is not constant.

Let F be the incoming frequency, F1 the oscillation generator frequency, and F2 the beat frequency. The frequency changer is so arranged, as before-explained, that its output is a definite multiple of the beat frequency input thereto. Consequently, if F2 is the beat frequency, and 100 the factor by Which the frequency changer multiples the beat frequency,

T05 by substitution,

:1- (1+10o) F1 i 100 Since the factor 100 is so chosen as to be a constant K, the lformula for the local source frequency becomes The device for producing a local frequency controlled by the incoming signal may take the form of an alternator, the speed of rotation of which is controlled by the incoming frequency. Since the number of poles is a constant, and the rotation is made to vary With the incoming frequency, the output of the alternator may thus be made to have the desired frequency ratioV to the incoming frequency.

A relay system constructed according to our invention has very many advantages. The frequency radiated may be kept substantially the same as the incoming frequency With but very little attention. The oscillation generator used for local heterodyning must of course be carefully set to the exact frequency desired but when this is done, the re-radiation4 of the same frequency as that received follows automatically.

Because the lines connecting the transmitting With the receiving stations carry only a comparatively low frequency, there will be but little loss in these lines. Feedback troubles between both the receiving antenna and the connection lines and between these lines and the ransmitting antenna are practically eliminated.

Inasmuch as, the various steps of amplification, which of necessity must be located within a limited enclosure, operate at different frequencies, but little trouble is experienced from undesired oscillations caused by regeneration.

It is also feasible in our system to reradiate at any harmonic of the intermediate frequency, if desired, although in our preferred form we re-radiate at the same frequency as that of the received signal.

Numerous other advantages of our system will be apparent to those skilled in the art, as will also many modifications thereof. Although we have illustrated and described herein but one specific embodiment of our invention, we are fully aware that such other' modifications are possible and do not intend to be limited except insofar as is necessary by prior art or as indicated by the appended claims. l

l/Ve claim as our invention:

l. In a relay system, means for receiving signals at radio frequency, means for changing said signals to a lower super-audible frequency, and means comprising a frequency changer for raising said super-audible frequency to a radio-frequency for retransmission.

2. In a relay system, means for receiving signals at radio frequency, means for deriving a super-audible frequency from said radio-frequency that bears a harmonic relation thereto, and means for deriving a radiofrequency from said super-audible frequency that bears a harmonic relation thereto.

In a relay system, radiant energy receiving means, radiant energy transmitting means controlled thereby, means interposed therebetween whereby the frequency of incoming signals may be changed to a subharmonic of said frequency before being used to control the transmitting means, and means adjacent said transmitting means for deriving a radiation frequency from said sub-harmonic.

l. In a relay system, radio-frequency sig- `nal receiving means, signal transmitting means adapted to be controlled thereby, means interposed therebetween for producing a sub-harmonic of the signal frequency,

and means for deriving a radiation frequency from said sub-harmonic.

5. In a radio relay system, means for receiving signals at radio frequencies, transmitting means controlled thereby, and means interposed therebetween for producing from the incoming signal a sub-harmonic thereof and for raising the frequency of said subharmonic to a radio frequency suitable for re-radiation.

6. In a radio relay system, means for receiving signal frequencies, means for deriving sub-harmonic frequencies therefrom, means directly controlled by said sub-harmonic frequencies, for producing the original frequencies, and signal radiating means controlled thereby.

7. In a. radio relay system, radio-frequency signal receiving means, heterodyne means for deriving a beat frequency from the received signal, means for deriving a harmonic of said beat frequency, and means for radiating said harmonic.

8. In a radio relay system signal receiving means, heterodyne means for deriving a beat frequency from received siGnals, means for deriving a harmonic of said beat frequency, and means for re-radiating said harmonic.

In a radio relay system comprising a plurality of stages adapted to amplify at different frequencies, piezo-electric means interposed between successive stages for impressing on the following stage a harmonic of the frequency to which the preceding stage is tuned.

l0. In a radio relay system, a plurality of amplifying stages tuned to differing super-audible frequencies, and frequency changing means comprising a piezo-electric crystal serving as a coupling device between certain of said stages.

ll. The method of relaying signals of substantially radio frequency comprising the steps of changing said signals to signals of a frequency bearing the relationship of a sub-harmonic of the initial frequency, amplifying said signals of the sub-harmonic frequency and subsequently restoring said signals to their initial radio-frequency condition.

In testimony whereof, we have hereunto subscribed our names this 3rd day of September, 1926.

FRANK B. FALKNOR.

THADDEUS R. GOLDSBOROUGH.

ini 

